It was lucky, thought Poirot as he made the tour of the house and had many species of spider, plant and fish pointed out to him, that he was an appreciator of art. As far as the rivalry between St. John Wallace and Nancy Ducane went, he knew what he thought about that. Wallace’s pictures were meticulous and worthy, but they made one feel nothing. Nancy Ducane’s was the greater talent. She had encapsulated the essence of Louisa Wallace and made her live on canvas as vividly as she lived in real life. Poirot found himself wanting to look at the portrait again before he left the house, and not only to check that he was not mistaken about the important detail he thought he had noticed.

Dorcas appeared on the upstairs landing. “Your coffee, sir.” Poirot, who had been inside St. John Wallace’s study, stepped forward to take the cup from her hand. She lurched back as if she hadn’t expected him to move toward her, and spilled most of the drink on her white apron. “Oh, dear! I’m sorry, sir, I’m a right old butterfingers. I’ll make you another cup.”

“No, no, please. There is no need.” Poirot seized what was left of his coffee and ingested it in one gulp, before any more of it could be spilled.

“This one is my favorite, I think,” said Louisa Wallace, still in the study. She was pointing at a painting that Poirot couldn’t see. “Blue Bindweed: Solanum Dulcamara. The fourth of August last year, you see? This was my wedding anniversary present from St. John. Thirty years. Beautiful, isn’t it?”

“Are you sure you wouldn’t like another cup of coffee, sir?” said Dorcas.

“The fourth of . . . Sacré tonnerre,” Poirot murmured to himself as a feeling of excitement started to grow inside him. He returned to the study and looked at the picture of blue bindweed.

“He has answered that question once, Dorcas. He does not want more coffee.”

“It’s no trouble, ma’am, honest it isn’t. He wanted coffee, and there was nothing left in the cup by the time he got it.”

“If nothing is there, one sees nothing,” mused Poirot cryptically. “One thinks of nothing. To notice a nothing—that is a difficult thing, even for Poirot, until one sees, somewhere else, the thing that should have been there.” He took Dorcas’s hand and kissed it. “My dear young lady, what you have brought to me is more valuable than coffee!”

“Ooh.” Dorcas tilted her head and stared. “Your eyes have gone all funny and green, sir.”

“Whatever can you mean, Monsieur Poirot?” Louisa Wallace asked. “Dorcas, go and get on with something useful.”

“Yes, madam.” The girl hurried away.